Transducers convert signals from one domain to another and are often used in sensors. A common sensor with a transducer that is seen in everyday life is a microphone, a sensor for audio signals with a transducer that converts sound waves to electrical signals.
Microelectromechanical system (MEMS) based sensors include a family of transducers produced using micromachining techniques. MEMS, such as a MEMS microphone, gather information from the environment through measuring physical phenomena, and electronics attached to the MEMS then process the signal information derived from the sensors. MEMS devices may be manufactured using micromachining fabrication techniques similar to those used for integrated circuits.
Audio microphones are commonly used in a variety of consumer applications such as cellular telephones, digital audio recorders, personal computers and teleconferencing systems. In a MEMS microphone, a pressure sensitive diaphragm is disposed directly onto an integrated circuit. As such, the microphone is contained on a single integrated circuit rather than being fabricated from individual discrete parts.
MEMS devices may be formed as oscillators, resonators, accelerometers, gyroscopes, pressure sensors, microphones, micro-mirrors, and other devices, and often use capacitive sensing techniques for measuring the physical phenomenon being measured. In such applications, the capacitance change of the capacitive sensor is converted into a usable voltage using interface circuits. In many applications, large amplitude physical signals caused by shock or similar events can overload the MEMS device and permanently or temporarily affect performance. In a MEMS microphone, shock events may affect an amount of charge on the capacitive plates. The performance of the MEMS, and especially the sensitivity, is related to the amount of charge on the capacitive plates. Thus, interface circuits for MEMS microphones are generally designed with charge biasing in mind.